1. Field of the Invention
The present invention relates to yellow pigment compositions for image recording, and processes for producing the same. More particularly, the present invention relates to yellow pigment compositions for image recording for use in color image formation in electronic photographs, electrostatic printing processes, ink jet systems and the like, and processes for producing the same.
2. Description of the Related Art
In color image formation in electronic photographs, electrostatic printing processes, ink jet systems and the like, the following characteristics, i.e., optical characteristics such as hue, transparency, tinctorial strength and the like, as well as durability such as light resistance, heat resistance, solvent resistance and the like are required in order to achieve reproducibility of color imaging which exhibits favorable quality. In addition, also characteristics involving absence of problems in connection with mutagenicity which results from the coloring agent, safety of decomposed products and the like are concomitantly required. Hence, it is preferred that the coloring agent for use is a pigment rather than a dye in general, in light of durability. Examples of the yellow pigment which has been used include e.g., benzidine based disazo pigments such as C. I. Pigment Yellow 12, 13, 17 and 831; condensed azo pigments such as C. I. Pigment Yellow 93, 95, 128, 151, 154, 155 and 180.
However, the benzidine based disazo pigments are preferable in respect of reproducibility of a color image which is predominantly affected by optical characteristics such as hue, transparency, tinctorial strength and the like, but is not preferable in respect of image retaining capacity which is predominantly affected by light resistance. Further, safety thereof is also in question due to decomposition products resulting from the benzidines. On the other hand, condensed azo pigments are satisfactory in retaining capacity of images and safety in comparison with benzidine based disazo pigments, however, they have drawbacks such as high cost, insufficient reproducibility of a color image and the like, with additional problems of dispersibility. Hence, they have good and bad points, respectively, under the present circumstances.
As a process for improving dispersibility of an azo pigment, for example, use of an azo based dispersion has been proposed (Patent Document 1:JP-A No. 7-126546). However, this azo based dispersion is effective in instances where the particle size of the pigment in paints, inks and the like is 1 to 20 μm, but the dispersing effect is not sufficient in color image formation in electronic photographs, electrostatic printing processes, ink jet systems and the like, because pigments for use therein have a further smaller particle size.